The present invention relates to propulsion in aeronautics and astronautics and, in particular, it concerns a deployable propulsion system and methods that can be used for a combined aircraft/spacecraft.
It is known that aircraft employ atmospheric propulsion systems that typically combine liquid fuel that is burnt with atmospheric oxygen to provide power and/or thrust for flight. Propulsion systems which operate in this way include: internal combustion engines (typically powering propellers); and an array of jet engines such as turboprops, fan gas turbines, ram jets and scram jets. In the specification and in the claims that follow, “jet engine” means any of the aforementioned or other variations of gas turbine engines. A reference for various jet and rocket engines, including other technological and general considerations, may be found in “The Standard Handbook for Aeronautical and Astronautical Engineers”, by Davies (2002), whose disclosure is incorporated herein by reference. Because atmospheric propulsion systems utilize atmospheric oxygen, most aircraft utilizing such propulsion systems are limited to operation up to altitudes ranging from approximately 45,000 to 65,000 feet or less, depending on the specific type of system and respective system operating conditions. The wide and approximate altitude range noted above, in the following description, and in the claims which follow is referred to as an “upper altitude range”.
Rocket engines, as opposed to typical aircraft propulsion systems, combine fuel (usually a fluid in liquid form, but sometimes in solid form) which is burnt with oxygen (usually in the form of an oxidizer fluid), both of which are stored and carried in the rocket, to produce thrust for flight. In the specification and in the claims that follow, “rocket engine” means any type of a rocket engine whether having liquid, solid, or gaseous fuel and oxidizer configurations. Because all of its fuel and oxidizer are carried “on-board”, a rocket propulsion system does not need atmospheric oxygen and may be operated: in an atmosphere; at altitudes near or above the upper altitude range, or in outer space. However, since rocket propulsion systems must have all of their fuel and oxidizer carried on board, in addition to the necessary rocket engine components, there is a serious consideration of increased flight weight when compared to typical aircraft propulsion systems. One way of dealing with the increased weight is to incorporate disposable subsystems or to make the entire rocket propulsion system disposable once it has been operated for a specific purpose or mission. Disposability of subsystems or a disposable overall system typically contributes to increased cost. In general, and because of all of these reasons, atmospheric propulsion systems are much more widely preferred over rocket propulsion systems for atmospheric flight. Therefore, rocket propulsion systems are usually limited to non-atmospheric flight, meaning flight at very high altitude or in space.
An interesting consideration arises for a craft that is to be flown in the atmosphere and above the atmosphere and whose propulsion system or systems is/are not disposable. Labatut et al., in U.S. Pat. No. 5,052,176, whose disclosure is incorporated herein by reference, describe a propulsion system for a reusable spacecraft having a turbojet, ramjet, and rocket modes of operation. Hydrogen or exhaust gases from a gas generator drive a gas turbine, which powers an air compressor in the turbojet mode. An injection device injects hydrogen and exhaust from the gas driven turbine in the combustion chamber in the turbojet mode. In the ramjet mode, only hydrogen is injected into the combustion chamber. In the rocket mode, hydrogen and oxygen are supplied to the rocket motor. An adjustable nozzle is provided to form a variable throat convergent-divergent nozzle in the turbojet and ramjet modes and to form a divergent nozzle in the rocket mode
The idea of a craft having a combined jet and rocket engine is disclosed in U.S. Pat. No. 5,159,809 by Cias and Hermant, whose disclosure is incorporated herein by reference. Cias and Hermant describe a combined propulsion engine comprising a jet and rocket engine. The jet engine comprises an air inlet device and an external nozzle which, in association with a central body, defining an air-breathing combustion chamber, while the rocket engine comprises a non-air-breathing annular combustion chamber and at least one turbo pump for feeding it with propellant. The combustion chamber of the rocket engine is disposed inside the rear of a central body and it is situated at the downstream end of the air-breathing combustion chamber. The rocket engine combustion chamber is itself delimited by a streamlined portion extending along the central body and constituting a spike, which penetrates into the throat of the external nozzle while ensuring aerodynamic continuity for the stream of combustion gases leaving the air-breathing combustion chamber. The combined engine is capable of operating alternately or simultaneously, depending on the stage of a flight.
When separate jet and rocket engines are employed in a combined aircraft/spacecraft, a distinct disadvantage is that the respective engines occupy extra space when, for example, they are mounted on the wings or externally to the fuselage of an aircraft/spacecraft. In addition to the consideration of extra space occupied by respectively externally mounted engines, another more serious disadvantage is that of additional drag caused by the rocket engine, typically not operated in lower altitudes, upon the aircraft/spacecraft when it is flown in an atmosphere.
A combined jet and rocket engine configuration, while offering an advantage of space and drag savings, due to the functioning of both the jet and rocket engine within the same fairing, has an apparent disadvantage in that such a configuration requires a special engine design, undoubtedly leading to unconventional manufacturing considerations. The use of separate, conventional respective jet and rocket engines would be advantageous from a standpoint of overall implementation of a combined jet and rocket propulsion system and from a standpoint of the reliability and safety gained by using more conventional and tested subsystems.
There is therefore a need for a deployable propulsion system for a combined aircraft/spacecraft wherein separate jet and rocket engines may be deployed to occupy substantially the same space when in operation.